Manufacturing of new potential plaster molds for slip casting of alumina nanoparticles

Abstract

Plaster molds were made using α- and β-forms of hemihydrate plaster as raw materials and melamine formaldehyde sulfonate (MFS) as retarder. Effects of plaster to water (P/W) ratio on physical and mechanical properties of the manufactured molds including density, apparent porosity, fluidity, flexural strength, and casting rate were investigated. Primary results showed that α-hemihydrate is more compatible with increased P/W ratio than β-hemihydrate, while the addition of MFS promotes β-hemihydrate compatibility with increased P/W ratio that provides the proper condition for changing the porosity and controlling the casting rate. For measuring casting rate, slips containing alumina nanoparticles were prepared with 35 wt% solid content using Tiron (C6H4Na2O8S) and polyvinyl alcohol (PVA) as dispersant and binder, respectively. Results revealed that the fluidity, density, flexural strength, and casting rate of α-hemihydrate plaster are higher than β-hemihydrate plaster. Due to the improved diffusion rate of alumina nanoparticles in relevant slips, the porosity of the plasters should be controlled in accordance with the nanoparticles size. Results confirmed that α-plaster molds have better characteristics in this regard. After casting in α- and β-hemihydrate plaster molds, specimens were sintered at 1600 °C for 2 h. Hereon samples cast in α-hemihydrate plaster mold showed higher density.